First Season Episodes - Invaders From The Fifth Dimension (episode 8)

An alien spaceship, run by luminous pilots from the fifth dimension, invades the Robinson space colony in search of a humanoid brain to replace their guidance control computer.

A blip is detected on the Robinson's scanner warning of an alien spacecraft's descent. Judy and Maureen call Will, but the blip disappears and Will dismisses it as a figment of their imagination. Meanwhile, Smith observes the craft from behind some rocks. When he tries to run away, a beam issues from the small round ship and freezes him in his steps. An alien voice explains that a humanoid brain is needed to replace a worn circuit in their guidance control system. Smith is suddenly scooped inside the limbo interior of the craft and an alien voice explains that they may have to reduce his size to fit him into the ship. Smith says that he can obtain a smaller humanoid for them. The aliens release the doctor, but not without materializing a glowing band around his neck -a device which will kill him if he does not return in one day. Smith discovers that Will has gone rock hunting at a lava bed. Maureen and Judy describe the blip they saw and Don and Penny describe Smith's strange behavior.

Sending Don southward on the rocket belt, John heads out in the Chariot with Maureen and the Robot. Meanwhile, Smith persuades Will to help him infiltrate the strange spacecraft. When John's voice is heard calling for Will, Smith convinces the boy that they must not answer or their efforts will be lost. Maureen catches a glimpse of the alien craft, but it dematerializes before her eyes. Will and Smith keep moving. Suddenly, Will is teleported inside the alien spacecraft and the creatures begin testing his brain. Smith finds the Chariot and leads John and Maureen to the ship. Inside, Will sees his parents on the viewing screen. He begs the aliens not to hurt them. The Luminary disgustedly orders Will's release -his brain is too primitive. One of the other aliens warns that they have built up too much lift-off power to let Will go. But the Luminary does not listen; the alien craft lifts off and disintegrates in mid-air. 

Recovering Will, who was left on the ground, everyone heads back to the Jupiter 2 where, sometime later, Don is nearly crushed during an earthquake.

Filming